Fatal error: Uncaught Error: Interface "Drupal\Core\Cache\Context\CacheContextInterface" not found in /home/www/drupal8/test/core/lib/Drupal/Core/Cache/Context/SessionExistsCacheContext.php:14 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/lib/Drupal/Core/Cache/Context/SessionExistsCacheContext.php on line 14